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Roller Chain Latch Mechanism

  1. Feb 19, 2015 #1
    I'm looking for a simple latch design. My project will have two roller chain sprockets positioned one above the other with about a two foot gap. A motor will turn one of the sprockets and the other is just an idler sprocket. A #40 roller chain will run around the two sprockets. Mounted just beside this chain and sprocket setup, will be a vertical slider rail with an object that travels up and down the rail.

    I need something attached to a chain link(s) that will circle the bottom sprocket, latch onto the object on the slider rail, drag/lift the object upwards, then release(drop) the object before, at, or while the chain link carries around the top sprocket. The latch mechanism must then again latch the object next time around the bottom sprocket and repeat the latch/lift/drop cycle indefinitely.

    I am looking for a simple design without incorporating additional motors or electronics if possible. I can add additional levers/pulleys or anything necessary. Please let me know. Thanks so much!
  2. jcsd
  3. Feb 19, 2015 #2


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    Staff: Mentor

    Welcome to the PF.

    How heavy is the object to be lifted, and how big is it? Do you really need a latch, or could it just be a cup to pick up and drop off the object?

    Do you have any conceptual drawings yet? I looked around Google Images some, but didn't have quite the right search terms yet. Perhaps you will have better luck...

  4. Feb 20, 2015 #3


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    Science Advisor

    If you replace one of the roller pins with a longer pin, an object with two slightly curved arms can catch on the long pin and be raised until it reaches the top sprocket when the roller chain pin will move away and so disengage from the arms.
    If the object falls down the rail quickly you can use two long pins, equally spaced in the one chain, to double the rate of lift and drop.
  5. Feb 20, 2015 #4
    I have attached a picture as per Berkeman's suggestion. The weight could be as much as 10 lbs. I'm hoping a single link on a chain has that much strength, otherwise I use a more robust chain.

    I have thought of just that. However, if I'm understanding you properly, the problem is when the link travels around the upper sprocket, the pin won't "slide" away horizontally to disengage from the curved arms. The pin will remain at 90 degrees to the chain link and will follow the sprocket so it will travel up and point vertical then continue traveling down and point horizontal again pointing in the other direction, thereby hooking onto an not releasing the curved arm..
    However, that gave me an idea. I have a special chain link which contains a small bracket. If I attach a U shaped pin to the link, as in my 2nd diagram, the arm on the slider will slide off the U shaped pin nicely I think.

    Oh wait, if you meant the curved arms to be curved vertically, then yes you are 100% correct as the pin will slide along the curved surface until it's released, same as what I drew only the switch the pin onto the chain and the curved bracket onto the sliding piece.

    Yes, this is solved....thanks so VERY MUCH!!!! Greatly appreciated!

    Chain & Sprocket Diagram.jpg Chain & Sprocket Diagram 2.jpg
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